Three points:
You can't correct a 2021 W-2 at this point because the withheld 2021 taxes have long been deposited with the state (by your employer). Therefore the original W-2 is correct.
If you continued to work in CA after moving to NV, then all 12 months of your work income is taxable by CA. CA can tax you as a non-resident for work actually performed within CA.
If you did not work in CA after your move, then you should file a part-year resident CA return on which you allocate to CA only your earnings as a CA resident. On that return you should enter your W-2 as is. If CA questions your return, you can explain what happened.
Your situation is not that unusual. Employers make mistakes with withholding all the time when employees move from one state to another.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
